The effect of C/N ratio on bacterial community and water quality in a mussel-fish integrated system

Abstract

A 30‐day experiment was conducted to evaluate the effect of C/N ratio on water quality and bacterial community in an integrated system comprising one molluscan species (pearl mussel Hyriopsis cumingii) and two fish species (gibel carp Carassius gibelio and silver carp Hypophthalmichthys molitrix) at five C/N ratios (6, 8, 10, 12 and 14). The mussel and fishes were reared in the experimental tanks (400 L), but gibel carp received formulated feed. Water quality in the experimental tanks was analysed on day 0, 10, 20 and 30, and bacterial community in the water column and sediment was analysed on day 30. Total nitrogen, total phosphorus and total organic carbon accumulated in the tanks over time. Ammonia and nitrite decreased with the increase in C/N ratio. Bacterial community in the water column and sediment changed at the phylum and genus levels with the increase in C/N ratio, and the critical C/N ratio causing a functional shift of bacterial community occurred at 10 in water column and 12 in sediment. The increase in C/N ratio benefited the growth of both potential probiotics and pathogenic bacteria. The high C/N ratio enhanced the bacterial functions of chemoheterotrophy and hydrocarbon degradation, but depressed the functions of nitrification and denitrification in the water column and sediment respectively. This study reveals that the C/N ratio can be used as a tool to manipulate the bacterial community and water quality in the mussel‐fish integrated system.

Effects of microbial products and extra carbon on water quality and bacterial community in a fish polyculture system

“…Zheng et al. () reported that increasing C/N ratio benefited to improve water quality in a mussel‐fish integrated system. Results of the present study revealed that extra carbon (glucose) addition should be a way to reduce accumulation of ammonia, nitrite and nitrate in fish polyculture.…”

“…Zheng et al. () reported that C/N ratio could affect bacterial community in a mussel‐fish integrated system. In the present study, adding glucose on the 40th day, 46th day and 52th day resulted in significant change of C/N ratio on the 55th day.…”

“…® Water DNA kit (Omega Bio‐Tek, Norcross, USA). Bacterial V4‐V5 hypervariable regions of 16S rRNA gene were amplified with the specific universal primer pairs 515F–907R (Zheng et al., ), and PCR was performed with ABI GeneAmp ® 9700 using TransStart Fastpfu DNA Polymerase (TransGen Biotech, Beijing, China). The PCR reaction mixture (20 μl) comprised 4 μl 1× FastPfu Buffer, 2.5 mM dNTPs, 5 μM each of forward and reverse primers, 1 unit FastPfu Polymerase (2.5 unit per μl) and 10 ng DNA template.…”

“…Generally, three ways are used for microbial manipulation, including (a) supplementation of exogenous bacteria (Liang et al., ; Wu et al., ; Zhang et al., ), (b) adding the nutrients that benefit growth of the preferred bacteria (Avnimelech, ; Gao, Shan, Zhang, Bao & Ma, ; Xu, Morris & Samocha, ; Yu et al., ; Zheng, Zhang, Qin & Wang, ) and (c) adding exogenous bacteria and nutrients in combination (Hu et al., ). The outcomes of exogenous bacteria in improving production performance and water quality of aquaculture practices are inconsistent.…”

“…Zheng, Tang, Zhang, Qin and Wang (2017) indicated the role of four commercial microbial products in regulating water quality in a mussel-fish integrated system might be associated with the environmental background. Ratio of carbon to nitrogen (C/N ratio) has been demonstrated a critical factor that regulates bacterial community and water quality in aquaculture systems (Avnimelech, 1999;Gao et al, 2012;Xu et al, 2016;Yu et al, 2016;Zheng et al, 2018). For instance, C/N ratio affected the competition between autotrophic bacteria and heterotrophic bacteria (Ebeling, Timmons & Bisogni, 2006) and relative abundance of potential probiotics or pathogens (Aguilera-Rivera et al, 2014;Ferreira et al, 2015;Murray & Peeler, 2005;Yu et al, 2016;Zheng et al, 2018).…”